LOCOS with sidewall spacer for different capacitance density capacitors

ABSTRACT

An integrated circuit (IC) includes a first capacitor, a second capacitor, and functional circuitry configured together with the capacitors for realizing at least one circuit function in a semiconductor surface layer on a substrate. The capacitors include a top plate over a LOCal Oxidation of Silicon (LOCOS) oxide, wherein a thickness of the LOCOS oxide for the second capacitor is thicker than a thickness of the LOCOS oxide for the first capacitor. There is a contact for the top plate and a contact for a bottom plate for the first and second capacitors.

FIELD

This Disclosure relates to integrated circuits having LOCOS capacitors.

BACKGROUND

LOCal Oxidation of Silicon (LOCOS) is a semiconductor fabrication process that uses a patterned oxygen diffusion barrier layer, commonly a silicon nitride layer over areas not meant to be oxidized, where a thermally grown silicon dioxide layer is formed in etched apertures in the oxygen diffusion barrier layer at a given thickness, with a thinner tapered silicon oxide region being formed along the edges of the oxygen diffusion barrier layer. A Si-silicon oxide interface is formed at a lower point than the rest of the silicon surface. Some capacitors utilize a LOCOS oxide as their dielectric. Although the active areas widths bordered by a LOCOS oxide can be varied, LOCOS like other oxide growth processes provide a single given oxide thickness across the die and across the wafer.

SUMMARY

This Summary is provided to introduce a brief selection of disclosed concepts in a simplified form that are further described below in the Detailed Description including the drawings provided. This Summary is not intended to limit the claimed subject matter's scope.

Disclosed aspects include an integrated circuit (IC) formed in a semiconductor surface layer on a substrate that includes a first capacitor and a second capacitor. The first and second capacitors include top plate over a LOCOS oxide, wherein the thickness of the LOCOS oxide for the second capacitor is thicker than the thickness of the LOCOS oxide for the first capacitor. There is a contact for the top plate and a contact for a bottom plate for both the first and second capacitors.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference Will Now be Made to the Accompanying Drawings, which are not Necessarily Drawn to Scale, Wherein:

FIG. 1 is a cross sectional depiction of an example IC including a first and a second LOCOS capacitor that have different LOCOS oxide thicknesses to provide different capacitance densities, according to an example aspect.

FIGS. 2A-2F are cross-sectional diagrams showing processing progression for an example method of forming an IC having including a first and a second planar LOCOS capacitor having different capacitance densities, according to an example aspect.

FIGS. 3A-3G are cross-sectional diagrams showing processing progression for an example method of forming an IC including a first and a second trench LOCOS capacitor having different capacitance densities, according to an example aspect.

FIGS. 4A-4F are cross-sectional diagrams showing processing progression for another example method of forming an IC having a first planar LOCOS capacitor and a second trench LOCOS capacitor that have different capacitance densities, according to an example aspect.

DETAILED DESCRIPTION

Example aspects are described with reference to the drawings, wherein like reference numerals are used to designate similar or equivalent elements. Illustrated ordering of acts or events should not be considered as limiting, as some acts or events may occur in different order and/or concurrently with other acts or events. Furthermore, some illustrated acts or events may not be required to implement a methodology in accordance with this disclosure.

Also, the terms “coupled to” or “couples with” (and the like) as used herein without further qualification are intended to describe either an indirect or direct electrical connection. Thus, if a first device “couples” to a second device, that connection can be through a direct electrical connection where there are only parasitics in the pathway, or through an indirect electrical connection via intervening items including other devices and connections. For indirect coupling, the intervening item generally does not modify the information of a signal but may adjust its current level, voltage level, and/or power level.

Disclosed aspects recognize it is desirable to be able to form different capacitance density (capacitance/unit area) capacitors using a single masking level and a single patterning step. For some power transistors integrated into a Bipolar Complementary Metal Oxide Semiconductor (BiCMOS) process, this presents a cost and/or complexity problem, because multiple different capacitance density capacitors are needed to co-exist in the same technology, including in some cases on the same IC product. It is also recognized that known LOCOS approaches like other oxidation processes have the disadvantage of only providing a single oxide thickness. This Disclosure describes a LOCOS oxidation process flow that utilizes sidewall spacers to produce two or more distinct LOCOS oxide thicknesses.

Forming sidewall spacers in wider oxygen diffusion barrier (ODB) layer opening(s) over the semiconductor surface layer, but not forming sidewall spacers in a narrower width ODB layer opening(s) over the semiconductor surface enables creating at least two different LOCOS oxide thicknesses from a single mask level and patterning step. The thicker LOCOS oxide for planar LOCOS capacitors will be thicker in the thickest center region as well as in the thinner bird's beak region at the edge of the LOCOS oxide as compared to the thinner LOCOS oxide. Sidewall spacers (e.g., comprising silicon nitride) formed in a wider first ODB layer opening(s) but not in a narrower first ODB layer opening(s) creates two (or more) different LOCOS layer thicknesses, which thus depend on the width of the first ODB layer opening. The width of the wider first ODB layer opening (referred to herein as the 2^(nd) first ODB layer opening) is generally at least 0.05 μm wider than the width of the narrower first ODB layer opening (referred to herein as the 1^(st) first ODB layer opening).

FIG. 1 is a cross sectional depiction of an example IC 100 including a first trench capacitor 150 a and a second trench capacitor 150 b that have different LOCOS oxide thicknesses to provide different capacitance densities. The second trench capacitor 150 b can be seen to be considerable wider and have a significantly thicker LOCOS oxide 110 b thickness as compared to width and thickness of LOCOS oxide 110 a for the first trench capacitor 150 a. The trench capacitors 150 a, 150 b each have a top plate 112. The IC 100 also includes functional circuitry 180 shown as a block that comprises circuit elements (including transistors, and generally diodes, resistors, capacitors, etc.) formed in the semiconductor surface layer 106 of or on the substrate 102 that is configured together with the trench capacitors 150 a and 150 b for realizing at least one circuit function such as analog (e.g., an amplifier, power converter or power field effect transistor (FET)), RF, digital, or a memory function.

Although no field oxide is shown, IC 100 generally includes field oxide that may comprise a shallow trench isolation (STI) structure or the field oxide may also have a LOCOS oxide structure. A pre-metal dielectric (PMD) layer is shown as 159 and has thereunder a pad oxide layer as 158. Top side contacts are shown formed through the PMD layer 159 and the pad oxide layer 158 including contacts 122 a to the top plates 112 and contacts 122 b to the portion of the semiconductor surface layer 106 providing the bottom plates that have metal contacts 123 a, and 123 b shown as metal 1 (M1) contacts thereon. Top side contacts shown also include contacts 122 c to the functional circuitry 180 having M1 contacts 123 c thereon. Although the trench capacitor 150 a is shown having 2 trenches, and trench capacitor 150 b having one trench, disclosed trench capacitors can generally have any number of trenches.

FIGS. 2A-2G are cross-sectional diagrams showing processing progression for an example method of forming an IC including a first planar capacitor 180 a and a second planar capacitor 180 b that have different LOCOS oxide thicknesses to provide different capacitance densities. Referring to FIG. 2A, the in-process IC is shown after forming a 1st first ODB layer opening 164 a that is relatively narrower and a 2^(nd) first ODB layer opening 164 b that is relatively wider in a first ODB layer 160 that is on a pad oxide layer 158 layer which is on semiconductor surface layer 106 of a substrate 102. The ODB layer openings 164 a, 164 b are generally formed using a photoresist pattern as an etch mask and then etching apertures including a first width and at least a second width in the first ODB layer 160.

The substrate 102 may be formed by starting with a p-type silicon wafer, possibly with at least one epitaxial layer thereon, and forming a n-type buried layer by implanting n-type dopants such as antimony or arsenic at a dose of 1×10¹⁵ cm⁻² to 1×10¹⁶ cm⁻². A thermal drive process heats the wafer to activate and diffuse the implanted n-type dopants. A p-type layer for the semiconductor surface layer 106 may be formed on the wafer by an epitaxial process with in-situ p-type doping. The epitaxially formed material may be, for example 4 microns to 6 microns thick. Although not shown, there may be an n-type buried layer that overlaps a boundary between the original silicon wafer and the epitaxially grown material for the semiconductor surface layer 106. An average bulk resistivity of the p-type layer may be, for example, 1 ohm-cm to 10 ohm-cm. An optional p-type buried layer may be also formed in the case of a p-type semiconductor surface layer 106 by implanting boron at an energy, for example, of 2 mega-electron volts (MeV) to 3 MeV.

The pad oxide layer 158 may be, for example, 20 to 250 A thick, 100 A thick being typical, and may be formed by thermal oxidation or by any of several chemical vapor deposition (CVD) processes. The first ODB layer 160 may include, for example, silicon nitride, such as formed by a low pressure chemical vapor deposition (LPCVD) process using dichlorosilane and ammonia. Alternatively, silicon nitride for the first ODB layer 160 may be formed by decomposition of bis(tertiary-butyl-amino) silane (BTBAS). Other processes to form the first ODB layer 160 are possible.

The etch mask may include photoresist formed by a photolithographic process, and may also include hard mask material such as amorphous carbon, and may include an anti-reflection layer such as an organic bottom anti-reflection coat (BARC). The exposed area of the top surface of the semiconductor surface layer 106 is defined by the 2^(nd) first ODB layer opening 164 b for the second planar capacitor 180 b has dimensions that are wider than a width of the 1^(st) first ODB layer opening 164 a for the first planar capacitor 180 a. The 2^(nd) first ODB layer opening 164 b is sufficiently wide so that after etching the second ODB layer 181 as described below relative to FIG. 2C a central portion of the etched area becomes cleared resulting in the formation of sidewall spacers, while the 1^(st) first ODB layer opening 164 a for the first planar capacitor 180 a has a width narrow enough so that after etching the second ODB layer 181 the entire 1^(st) first ODB layer opening 164 a remains covered with the second ODB layer 181. The first ODB layer 160 in areas exposed by the etch mask may be removed by a wet etch, for example an aqueous solution of phosphoric acid, which undercuts the etch mask. A portion of the pad oxide 158 may also be removed in the areas exposed by the etch mask.

Referring now to FIG. 2B, this FIG. shows results after growing a first LOCOS oxide layer 210, with a typical thickness of 200 to 1,000 A. The characteristic LOCOS oxidation bird's beak with a thinner LOCOS oxide at the edges under the first ODB layer 160 is shown.

An example furnace thermal oxidation process for growing a first LOCOS oxide layer 210 may include ramping a temperature of the furnace to about 1000° C. in a time period of 45 minutes to 90 minutes with an ambient of 2 percent to 10 percent oxygen, maintaining the temperature of the furnace at about 1000° C. for a time period of 10 minutes to 20 minutes while increasing the oxygen in the ambient to 80 percent to 95 percent oxygen, maintaining the temperature of the furnace at about 1000° C. for a time period of 60 minutes to 120 minutes while maintaining the oxygen in the ambient at 80 percent to 95 percent oxygen and adding hydrogen chloride gas to the ambient, maintaining the temperature of the furnace at about 1000° C. for a time period of 30 minutes to 90 minutes while maintaining the oxygen in the ambient at 80 percent to 95 percent oxygen with no hydrogen chloride, and ramping the temperature of the furnace down in a nitrogen ambient.

FIG. 2C shows results after depositing a second ODB layer 181 then a sacrificial sidewall film 182 on the second ODB layer 181 that functions as a sacrificial sidewall layer, then maskless etching of the sacrificial sidewall film 182 to form spacers 182 a in the 2^(nd) first ODB layer opening 164 b as it is sufficiently wide. The second ODB layer 181 is removed in the 2^(nd) first ODB layer opening 164 b because it is not protected by the sacrificial sidewall film 182. Sidewall spacers are not shown in the 1^(st) first ODB layer opening 164 a as it is narrower compared to the 2^(nd) first ODB layer opening 164 b, so that the 1^(st) first ODB layer opening 164 a is again shown as the sacrificial sidewall film 182 on the second ODB layer 181 in the 1^(st) first ODB layer opening 164 a.

FIG. 2D shows results after stripping the sacrificial sidewall film 182 and spacers 182 a which reveals spacers 181 a in the 2^(nd) first ODB layer opening 164 b. FIG. 2E shows results after growing a second LOCOS oxide layer resulting in an additional LOCOS portion shown as LOCOS 2 having a portion above and below the first LOCOS oxide layer 210, generally being 500 to 1,500 A of LOCOS 2 at the center of the wider 2^(nd) first ODB layer opening 164 b for the second planar capacitor 180 b, with no LOCOS 2 shown grown in the 1^(st) first ODB layer opening 164 a being a narrower opening due to the presence of the second ODB layer 181 over the whole opening.

Thus for the 1^(st) first ODB layer opening 164 a being narrower the sidewalls of the second ODB layer 181 remain merged so that only the first LOCOS oxidation process is able to oxidize the exposed silicon surface. This thinner LOCOS oxide is used to form all the oxide for the first planar capacitor 180 a. For the 2^(nd) first ODB layer opening 164 b being wider, the sidewalls are distinct (as shown as spacers 181 a in FIG. 2D) so that the second LOCOS oxidation can thicken the LOCOS layer by adding LOCOS 2 in the 2^(nd) first ODB layer opening 164 b. As with the first LOCOS oxide layer 210, the LOCOS 2 oxide will be tapered under the spacers 181 a, which is equivalent to a bird's beak region.

This completes the oxide thickness so that the LOCOS oxide is thicker for the second planar capacitator 180 b as it includes LOCOS oxide from both first LOCOS oxide layer 210 and the LOCOS 2 oxide as compared to the LOCOS oxide for the first planar capacitor 180 a that only includes the first LOCOS oxide layer 210. FIG. 2F shows results after removing the first ODB layer 160 and the second ODB layer 181 and then depositing a top plate layer, and patterning this top plate layer to form top plates 112, such as a top plate comprising polysilicon over the LOCOS oxide for the first and second planar capacitors 180 a, 180 b. Spacers 191 are shown on the sidewalls of the top plates 112.

FIGS. 3A-3G are cross-sectional diagrams showing processing progression for an example method of forming an IC including a first trench capacitor 350 a and a second trench capacitor 350 b having different LOCOS oxide thicknesses to provide different capacitance densities. FIG. 3A shows results after forming a 1^(st) first ODB layer opening 164 a (shown relatively narrower) and a 2^(nd) first ODB layer opening 164 b (shown relatively wider) in a first ODB layer 160 that is on a pad oxide layer 158 layer that is on a semiconductor surface layer 106 on a substrate 102. The ODB layer openings are generally formed by using a photoresist patterned etch mask and then etching the first ODB layer 160 to form the 1^(st) first ODB layer opening 164 a for the trench capacitor 350 a and the 2^(nd) first ODB layer opening 164 b for the trench capacitor 350 b. FIG. 3B shows the results after a silicon etch of the top surface of the semiconductor surface layer 106 after an oxide etch to remove pad oxide 158 in the 1^(st) and 2^(nd) first ODB layer opening openings 164 a, 164 b. A typical silicon etch depth is 100 A to 6,000 A.

FIG. 3C shows results after growing a first LOCOS oxide layer 210, with a typical thickness of 200 to 1,000 A. The characteristic LOCOS oxidation bird's beak is shown. FIG. 3D shows results after results after depositing a second ODB layer 181 then a sacrificial sidewall film 182 on the second ODB layer 181 that functions as a sacrificial sidewall layer, then maskless etching the sacrificial sidewall film 182 to form spacers 182 a in the 2^(nd) first ODB layer opening 164 b being relatively wider, but not forming sidewall spacers show as sacrificial sidewall film 182 over the entire 1^(st) first ODB layer opening 164 a being relatively narrower, and then removing the second ODB layer 181 where not protected by the sacrificial sidewall film 182. FIG. 3E shows results after results after removal of the sacrificial sidewall film 182 including spacers 182 a.

FIG. 3F shows results after growing a second LOCOS oxide layer in the 2^(nd) first ODB layer opening 164 b for the trench capacitor 350 b resulting in an additional LOCOS portion shown as LOCOS 2 above and below the first LOCOS oxide layer 210, generally being 500 to 1,500 A of LOCOS at the center of the wider 2^(nd) first ODB layer opening 164 b. There is no LOCOS 2 shown grown in the narrower first ODB layer opening 164 a due to the presence of the second ODB layer 181 over the whole opening.

Thus for the narrower 1^(st) first ODB layer opening 164 a the sidewalls of the second ODB layer 181 remain merged and only the first LOCOS oxidation process is able to oxidize the exposed silicon. This thinner oxide is used to form the LOCOS oxide for the trench capacitor 350 a. For the wider 2^(nd) first ODB layer opening 164 b, the sidewalls are distinct (as shown as spacers 182 a in FIG. 3D), so that the second LOCOS oxidation adds LOCOS 2 which thickens the LOCOS layer in the middle of the 2^(nd) first ODB layer opening 164 b for trench capacitor 350 b. The LOCOS oxide will be tapered under the spacers 182 a, which is equivalent to a bird's beak region that is controlled by the spacer thickness. This thicker LOCOS oxide is used to form the trench capacitor 350 b.

This completes the oxide thickness so that the LOCOS oxide is thicker for the trench capacitor 350 b as compared to the LOCOS oxide for the trench capacitor 350 a. FIG. 3G shows results after removing the first ODB layer 160 and the second ODB layer 181 and then forming a patterned top plate 112 that can comprise polysilicon over the LOCOS oxides for the trench capacitors 350 a and 350 b.

FIGS. 4A-4F are cross-sectional diagrams showing processing progression for another example method of forming an IC having including a first planar capacitor shown as 450 a and a second trench capacitor shown as 450 b having different LOCOS thicknesses, according to an example aspect. FIG. 4A shows results after forming a relatively narrower 1^(st) first ODB layer opening 164 a for the first trench capacitor and a relatively wider 2^(nd) first ODB layer opening 164 b for the second trench capacitor 164 b in a first ODB layer 160 that is on a pad oxide layer 158 layer that is on a substrate 102 having a semiconductor surface layer 106. This process generally comprises using a photoresist patterned etch mask and then etching the first ODB layer 160 to form the 1^(st) and 2^(nd) first ODB layer openings 164 a, 164 b.

FIG. 4B shows results after growing a first LOCOS oxide layer 210, with a typical thickness of 200 to 1,000 A. The characteristic LOCOS oxidation bird's beak is shown. FIG. 4C shows results after depositing a second ODB layer 181, then depositing a sacrificial sidewall film 182 on the second ODB layer 181 that functions as a sacrificial sidewall layer, then maskless etching of the sacrificial sidewall film 182 and the second ODB layer 181. In the 2^(nd) first ODB layer opening 164 b associated with the second trench capacitor 450 b as it is relatively wider, etching of the sacrificial sidewall film 182 forms the spacers 182 a shown which enables the maskless etching to etch the second ODB layer 181 away from the edges in the 2^(nd) first ODB layer opening 164 b to form spacers 181 a because the second ODB layer 181 is not protected there by the sacrificial sidewall film 182. Sidewall spacers are not shown in the 1st first ODB layer opening 164 a associated with the first trench capacitor 450 a as it is narrower so that after the maskless etching there is as a result the sacrificial sidewall film 182 on the second ODB layer 181 over the full area of the 1st first ODB layer opening 164 a.

FIG. 4D shows results after stripping the sacrificial sidewall film 182 in the 1st first ODB layer opening 164 a for the first trench capacitor 450 a and the spacers 182 a in the 2^(nd) first ODB layer opening 164 b for the second trench capacitor 450 b and then silicon etching in the exposed semiconductor surface layer 106 in the 2^(nd) first ODB layer opening 164 b, where the second ODB layer 181 extending over the entire 1^(st) first ODB layer opening 164 a for the first trench capacitor 450 a prevents any etching of the semiconductor surface layer 106. The silicon etch depth for the second trench capacitor 450 b can be 100 A to 30 μm, with a typical silicon etch depth being 500 A to 2 μm.

FIG. 4E shows results after growing a second LOCOS oxide layer resulting in an a LOCOS portion shown as LOCOS 2 above and below the first LOCOS oxide layer 210, generally being 500 to 1,500 A of LOCOS oxide at the center of the wider 2^(nd) first ODB layer opening 164 b for the second trench capacitor 450 b, with no LOCOS 2 shown grown in the narrower 1^(st) first ODB layer opening 164 a for the first trench capacitor 450 a due to the presence of the second ODB layer 181 over the whole opening.

Thus for the narrower 1^(st) first ODB layer opening 164 a for the first trench capacitor 450 a the sidewalls of the second ODB layer 181 remain merged and only the first LOCOS oxidation process is able to oxidize the exposed silicon. This thinner oxide is used to form the oxide for the first trench capacitor 450 a. For the wider 2^(nd) first ODB layer opening 164 b for the second trench capacitor 450 b, the sidewalls are distinct so the second LOCOS oxidation can grow in the middle of the 2^(nd) first ODB layer opening 164 b. The oxide will be tapered under the spacers 182 a, which is equivalent to a bird's beak region that is controlled by the spacer thickness. This thicker oxide is used to form the trench capacitor 450 b. FIG. 4E shows results after results after removal of the sacrificial sidewall film 182 including spacers 182 a. FIG. 4F shows results after removing the first ODB layer 160 and the second ODB layer 181 and spacers 181 a, and then forming a patterned top plate 112 that can comprise polysilicon over the LOCOS oxide for the trench capacitors 450 a, 450 b.

Described below is front-end-of-the-line (FEOL) MOS processing to complete formation of the capacitors comprising forming a top plate and contacts. A patterned layer of top plate material shown as 112 in FIG. 1 is formed over the layers of LOCOS oxide 110 a, 110 b. The top plate 112 may include, for example, polycrystalline silicon, referred to herein as polysilicon, possibly doped with n-type dopants. Polysilicon as the layer of top plate 112 may be, for example, 300 nanometers to 800 nanometers thick.

Disclosed aspects can be used to form semiconductor die that may be integrated into a variety of assembly flows to form a variety of different devices and related products. The semiconductor die may include various elements therein and/or layers thereon, including barrier layers, dielectric layers, device structures, active elements and passive elements including source regions, drain regions, bit lines, bases, emitters, collectors, conductive lines, conductive vias, etc. Moreover, the semiconductor die can be formed from a variety of processes including bipolar, Insulated Gate Bipolar Transistor (IGBT), CMOS, BiCMOS and MEMS.

Those skilled in the art to which this Disclosure relates will appreciate that many other aspects are possible within the scope of the claimed invention, and further additions, deletions, substitutions and modifications may be made to the described aspects without departing from the scope of this Disclosure. 

The invention claimed is:
 1. A method of fabricating an integrated circuit (IC), comprising: depositing a first oxygen diffusion barrier (ODB) layer on a pad oxide layer on a semiconductor surface layer on a substrate; patterning and then etching the first ODB layer to form a 1^(st) first ODB layer opening and at least a 2^(nd) first ODB layer opening, wherein a width of the 2^(nd) first ODB layer opening is larger than a width of the 1^(st) first ODB layer opening; growing a first LOCal Oxidation of Silicon (LOCOS) layer in the 1^(st) first ODB layer opening and in the 2^(nd) first ODB layer opening; depositing a second ODB layer and then depositing a sacrificial sidewall film on the second ODB layer; etching the sacrificial sidewall film to form a spacer in the 2^(nd) first ODB layer opening but not in the 1^(st) first ODB layer opening which remains blocked by the sacrificial sidewall film and removing the second ODB layer where not protected by the sacrificial sidewall film; stripping the sacrificial sidewall film; growing a second LOCOS layer in the 2^(nd) first ODB layer opening but not in the 1^(st) first ODB layer opening; removing the first and the second ODB layer, and forming a top plate over the first opening to complete a first capacitor and over the second opening to complete a second capacitor.
 2. The method of claim 1, wherein the first capacitor and the second capacitor both comprise planar capacitors.
 3. The method of claim 1, further comprising after the patterning and then etching the first ODB layer and before the growing the first LOCOS layer, etching the semiconductor surface layer in the first opening and in the second opening to a predetermined depth, wherein the first capacitor and the second capacitor both comprise trench capacitors.
 4. The method of claim 1, further comprising after the stripping the sacrificial sidewall film and before the growing the second LOCOS layer, etching the semiconductor surface layer in the second opening to a predetermined depth, wherein the first capacitor is a planar capacitor and the second capacitor is a trench capacitor.
 5. The method of claim 1, wherein a thickness of the first LOCOS layer is 200 to 1,000 A.
 6. The method of claim 1, wherein the first ODB layer and the second ODB layer both comprise silicon nitride.
 7. The method of claim 1, wherein the width of the 2nd first ODB layer opening is at least 0.05 μm greater than the width of the 1^(st) first ODB layer opening.
 8. The method of claim 1, wherein the first ODB layer comprises silicon nitride and is 300 to 2,000 A thick.
 9. The method of claim 1, wherein the top plate comprises polysilicon.
 10. A method of fabricating an integrated circuit (IC), comprising: depositing a first oxygen diffusion barrier (ODB) layer over a substrate; patterning and etching the first ODB layer to form a first opening and a second opening, wherein a width of the second opening is larger than a width of the first opening; forming a first oxide layer in the first opening and in the second opening, the first oxide layer having a thickness in the range of 200 Å to 1000 Å; depositing a second ODB layer and then depositing a sacrificial sidewall film on the second ODB layer; etching the sacrificial sidewall film to form a spacer in the second opening but not in the first opening which remains blocked by the sacrificial sidewall film and removing the second ODB layer where not protected by the sacrificial sidewall film; stripping the sacrificial sidewall film; increasing the thickness of the first oxide layer in the second opening while the first opening is covered by the second ODB layer; removing the first and the second ODB layers; and forming a top plate over the first opening to complete a first capacitor and over the second opening to complete a second capacitor, where the first oxide layer is thicker in the second capacitor than in the first capacitor.
 11. The method of claim 10, wherein the first capacitor and the second capacitor both comprise planar capacitors.
 12. The method of claim 10, further comprising after the patterning and then etching the first ODB layer and before the forming the first oxide layer, etching the substrate in the first opening and in the second opening to a predetermined depth, wherein the first capacitor and the second capacitor both comprise trench capacitors.
 13. The method of claim 10, further comprising after the stripping the sacrificial sidewall film and before the increasing a thickness of the first oxide layer, etching the substrate in the second opening to a predetermined depth, wherein the first capacitor is a planar capacitor and the second capacitor is a trench capacitor.
 14. The method of claim 10, wherein the first ODB layer and the second ODB layer both comprise silicon nitride.
 15. The method of claim 10, wherein the width of the second opening is at least 0.05 μm greater than the width of the first opening.
 16. The method of claim 10, wherein the top plate comprises polysilicon.
 17. The method of claim 10, wherein the first oxide layer is formed using a first LOCOS (LOCal Oxidation of Silicon) process.
 18. The method of claim 17, wherein increasing the thickness of the first oxide layer uses a second LOCOS process.
 19. A method of fabricating an integrated circuit (IC), comprising: forming a first oxide region and a second oxide region; forming an oxygen diffusion barrier over the first oxide region and only partially over the second oxide region; thermally oxidizing the second oxide region while the oxygen diffusion barrier remains over the first oxide region so that the second oxide region increases to a second thickness greater than a first thickness of the first oxide region; removing the oxygen diffusion barrier; and forming a top plate over the first oxide region to complete a first capacitor and over the second oxide region to complete a second capacitor.
 20. The method of claim 19, wherein forming an oxygen diffusion barrier over the first oxide region and only partially over the second oxide region comprises: depositing an oxygen diffusion barrier material over the first oxide region and the second oxide region; forming a sacrificial layer over the oxygen diffusion barrier material; etching the sacrificial layer to form spacers over the second oxide region, the etched sacrificial layer covering the first oxide layer; etching the oxygen diffusion barrier material where exposed by the sacrificial layer; and removing the sacrificial layer. 